This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from my applications entitled Error Correction Method of Vertical Scan Alignment for Shuttle Scanner filed in the Korean Industrial Property Office on Aug. 13, 1997 and there duly assigned Serial No. P97-38500 by that Office.
1. Field of the Invention
The present invention relates to a shuttle scanner and, more particularly, to a method for correcting a vertical alignment error in a shuttle scanner, using a shift correction value stored in a programmable read only memory (PROM).
2. Discussion of Related Art
Recently, multi-tasking systems that combine the various functions of a printer, a facsimile machine, a copy machine, a scanner, etc., have been developed. In combining scanner functions with a printer, a shuttle-type scanner using a shuttle scanner module is typically employed. The shuttle scanner module travels across the document original together with the ink cartridge, using the same driving system as that of the print head module. A shuttle scanner, however, has its own unique set of problems in performing a scanning operation.
For example, as shown in FIG. 1A, in scanning a document original using a shuttle scanner module, scanning is performed by dividing the sheet into 22xcx9c27 shuttle blocks, depending on the dimensions of the scanner module. In the scanning of a given shuttle block, as shown in FIG. 1B, a vertical trace or slice is scanned, with the scanner module moving across the sheet in a horizontal direction and proceeding with a sequential scanning of each slice until reaching the far edge of the sheet. Here, the 2,551st slice represents the final slice of a scanned block of a letter-sized sheet of paper, assuming a resolution of 300 dpi.
Meanwhile, in manufacturing a shuttle scanner, as with any such apparatus having many components, there is the unavoidable accumulation of assembly tolerances. Of particular concern is the assembly tolerance of a charge-coupled device which is mounted on a printed circuit board installed within the shuttle scanner module and which, by traveling across a document original, performs the actual scanning function via a slit formed in the bottom of the module. These tolerances must be minimized in order to maintain high quality image scanning, since each block is scanned individually to make up the entire image.
To illustrate this problem, a vertical line drawn down through the horizontally arranged blocks of a document original, as shown in FIG. 2A, is scanned. Due to the above-described assembly tolerances, a distorted reproduction such as that shown in FIG. 2B may result. That is, a slight skewing of the charge-coupled device with respect to the true vertical reference line (i.e., one having an infinite slope) as each block is scanned results in the scanned image being reproduced as if each block""s segment of the line were slanted. These slanted line segments start in the correct position at the top of each block, but a gradual shifting of the reproduced line, which is image distortion, is generated along the length of the slices of every block. The distortion (slant) may slope either to the right or to the left of vertical, depending on the incongruities and imperfections of a given scanner assembly.
Although high-precision manufacturing may be employed to minimize this problem, such tolerances will always exist to some degree. Besides, this solution leads to a sharp increase in product cost, and so a more practical solution is needed.
Accordingly, in order to overcome such drawbacks in the conventional art, it is therefore an object of the present invention to provide a method for compensating for the assembly tolerances in manufacturing a shuttle scanner.
It is another object of the present invention to provide a method for reducing the manufacturing costs of a shuttle scanner.
It is still another object of the present invention to provide a method for improving scanned image quality in a shuttle scanner.
It is yet another object of the present invention to provide a method for correcting a vertical alignment error occurring in a scanned image obtained by a shuttle scanner.
It is yet still another object of the present invention to provide a method for calculating a shift correction value in order to correct a vertical alignment error occurring in a scanned image obtained by a shuttle scanner.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, there is provided a method for correcting vertical alignment error in a shuttle scanner, comprising the steps of: (a) initializing a block count of a document to be scanned to a value of N; (b) scanning the Nth block and rasterizing the scanned block into a dot image; (c) shifting each dot of the dot image formed by the rasterized block according to a set of pre-stored correction values; and (d) incrementing the block count and performing the steps (b) through (d) until reaching the end of the document being scanned. The set of pre-stored correction values is produced by the steps of: scanning at least one block of a reference pattern formed on the document to be scanned; comparing the scanned reference pattern with an ideal reference line to thereby calculate a shift value for each dot of the scanned at least one block; and storing the calculated shift values in a memory device.
Accordingly, in the above method, a set of correction values is obtained for a given shuttle scanner at the time of manufacture, and the correction values are stored (programmed) in a memory device, e.g., a PROM, installed in the scanner itself. Thus, by comparing the unique program of each scanner with an ideal set of values representing a perfectly aligned construction with respect to a charge-coupled device traveling across a perfect paper feed path, the reproduced output of a scanned image can be corrected for any vertical alignment error.